Rheo.Backend.Mnesia (rheo v1.0.0)

Durable OTP :mnesia implementation of Rheo.Backend.

Always available (OTP :mnesia is an included application). Prefer when you want ETS-shaped tables that survive process restart on a single node without Mongo, Postgres, or Redis. Prefer Redis / Ecto Postgres / Mongo when several BEAM nodes must fetch the same group (distributed: false in v0.11).

Prefer the Rheo facade for application code. The opaque handle is this process's registered name (default Rheo.Mnesia), started via child_spec/1.

When to use

Single-node hosts that need durability across GenServer restart
Local / embedded deployments that already rely on OTP disk schema
Bridging from ETS prototypes without introducing an external database

Do not use for multi-node lease arbitration in v0.11 (distributed: false). Multiple Rheo instances on one node share the Mnesia schema but use unique table name prefixes.

Capabilities

durable: true — survives process restart when the Mnesia directory is kept
distributed: false — single-node disc_copies only (ADR 028)
batch_writes: true, ordered_range_scan: true
replay: true, partitions: true, contiguous_frontier: true
secondary_indexes: false — query/2 filters in-process
atomic_compare_and_set: false — dirty_write is not :mnesia.sync_transaction crash durability
notifications: false

Tables

ETS-shaped disc_copies tables under a per-handle prefix:

<prefix>.streams / .events / .groups / .deliveries
<prefix>.event_ids / .delivery_by_seq / .open_deliveries

Options

:name — handle / process name (default default_handle/0)
:dir — Mnesia directory (default under System.tmp_dir!/0)

Supervision example

children = [
  {Rheo, name: MyRheo, backend: {Rheo.Backend.Mnesia, dir: "/var/lib/rheo/mnesia"}}
]

Named handle:

children = [
  {Rheo,
   name: MyRheo,
   backend: {Rheo.Backend.Mnesia, name: MyRheo.Mnesia, dir: "/var/lib/rheo/mnesia"}}
]

Callback semantics are documented on Rheo.Backend.

Summary

Functions

child_spec(init_arg)

Child spec for the Mnesia GenServer (backend handle).

default_handle()

Default Mnesia handle name for the Rheo instance.

Functions

child_spec(init_arg)

@spec child_spec(keyword()) :: Supervisor.child_spec()

Child spec for the Mnesia GenServer (backend handle).

Arguments

opts — keyword options:
- :name — handle / process name (default default_handle/0)
- :dir — Mnesia directory (default under System.tmp_dir!/0)

Examples

iex> spec = Rheo.Backend.Mnesia.child_spec(name: :demo_mnesia, dir: "/tmp/rheo_mnesia_demo")
iex> {spec.id, elem(spec.start, 0), spec.type}
{{Rheo.Backend.Mnesia, :demo_mnesia}, Rheo.Backend.Mnesia, :worker}

Returns

A supervisor child spec map. The directory is created and the schema started when the GenServer initializes.

default_handle()

@spec default_handle() :: atom()

Default Mnesia handle name for the Rheo instance.

Examples

iex> Rheo.Backend.Mnesia.default_handle()
Rheo.Mnesia

Returns

A process name atom (Rheo.Mnesia).